No, a zebra danio cannot live alone. Zebra danios are schooling fish, so they seek safety and comfort in numbers. If kept alone, your zebra danio will be too scared to explore the tank and might stay in hiding most of the time.
Eventually, your lonely zebra danio will become stressed, lose its appetite, become ill, or even show aggression towards other fish.
You must keep at least five zebra danios together in a tank. Just make sure the tank is big enough for them.
In general, a single zebra danio requires two gallons of space in the tank. So a small school of five zebra danios needs a 10-gallon tank or larger to thrive.